Ignition timing control apparatus

ABSTRACT

An ignition timing control apparatus is disclosed which controls ignition timing of an internal combustion engine which is used with a marine vehicle. The apparatus, which controls ignition timing in dependence upon the opening degree of a throttle valve, includes a retardation moderating circuit for gradually changing the output of the throttle sensor when the throttle valve is driven in the closing direction, thereby preventing the engine from stalling during sudden decelerations of the engine.

TECHNICAL FIELD

The present invention relates to an ignition timing control apparatusfor changing the ignition timing of an internal combustion engine inaccordance with the opening degree of a throttle valve which operates toadjust the amount of intake air sucked into the engine.

BACKGROUND ART

Conventionally, ignition timing control apparatus have been known whichoperates to change ignition timing of an internal combustion engine inaccordance with the opening degree of a throttle valve which adjusts theamount of intake air sucked into the engine. In such ignition timingcontrol apparatus, ignition timing is controlled in proportion to thechange rate of the opening degree of a throttle valve as shown inFIG. 1. Specifically, as shown in FIG. 1(a), as the throttle openingchanges from the closed state toward the fully open state, ignitiontiming is controlled to advance as shown in FIG. 1(b). On the otherhand, as the throttle opening changes from the fully open state towardthe closed state, ignition timing is controlled to retard in proportionto the rate of change of the throttle opening.

With a marine vehicle, for example, equipped with such an ignitiontiming control apparatus, however, brake is often applied to suddenlydecelerate the vehicle by changing the engine operation from a forwarddrive into a rearward drive so as to make the propellant screw bladerevolve in a reverse direction. In this case, the engine is subjected toan abrupt increase in load because the screw blade is brought into therearward drive in spite of the marine vehicle still remaining in aforward driving state.

On the other hand, upon such a change in the drive condition of theengine, the opening degree of the throttle is normally in a fully closedstate and ignition timing is thus at the most retarded piston position,so the engine is easily caused to stall due to an abrupt change in theload on the engine.

The present invention is proposed to solve the above-described problems,and has for its object the provision of an ignition timing controlapparatus which is able to prevent a marine engine from being stalledupon rapid decelerations of a marine vehicle.

DISCLOSURE OF THE INVENTION

Specifically, the present invention comprises a throttle sensor foroutputting a voltlage which is in inverse proportion to the openingdegree of a throttle valve, a retardation moderating ciruit forreceiving the output signal of the throttle sensor and having a diodeconnected in parallel with a resistor of an integration circuit, anignition timing calculation circuit for outputting an ignition timingcontrol signal which advances in inverse proportion to the outputvoltage of the retardation moderating circuit, wherein when the throttleopening changes toward the closing direction, the output of theretardation moderation circuit is controlled to gradually increase sothat the ignition timing changes more gradually than the throttleopening does.

In addition, the present invention further comprises a timer circuit fordisabling the output of the ignition timing calculation circuit for apredetermined time from the engine starting period, and a compensationcircuit for increasing the output voltage of the retardation moderatingcircuit to a prescribed value so as to stabilize the engine operationduring engine starting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a characteristic view showing the relationship betweenignition timing and throttle opening in a conventional ignition timingcontrol apparatus;

FIG. 2 is a circuit diagram showing an ignition timing control apparatusof a first embodiment of the present invention;

FIG. 3 is a characteristic view showing the relationship betweenignition timing and throttle opening in the apparatus of FIG. 2;

FIG. 4 is a circuit diagram showing an ignition timing control apparatusof a second embodiment of the present invention; and

FIG. 5 is a circuit diagram showing a third embodiment of the presentinvention.

THE BEST MODE FOR EMBODYING THE PRESENT INVENTION

The present invention will now be described in detail with reference tothe accompanying drawings.

FIG. 2 shows a circuit diagram of an ignition timing control apparatusin accordance with first embodiment of the present invention. In thedrawings, reference numeral 1 designates a generator coil for a magnetowhich is adapted to be driven by an engine, the generator coil havingone end connected with an ignition capacitor 3 through a diode 2 and theother end connected to ground. Reference numeral 4 designates athyristor for discharging the capacitor 3 through an ignition coil 5,the thyristor constituting a switching element. Reference numerals 6 and7 designate the primary and secondary windings of the ignition coil 5.Reference numeral 8 designates a spark plug connected in series with thesecondary coil 7. Reference numeral 9 designates a counter electromotiveforce absorbing diode connected in parallel with the primary winding 6for absorbing a counter electromagnetic force of the ignition coil 5.Reference numeral 10 designates a biasing resistor connected between thegate and the cathode of the thyristor 4.

Further, reference numeral 11 designates a power circuit including adiode 12, a resistor 13 and a Zener diode 14 which are seriallyconnected with each other and which are connected between one end of thegenerator coil 1 and ground. A capacitor 15 is connected in parallelwith the Zener diode 14, with a junction between the Zener diode 14 andthe resistor 13 forming the output terminal of the power circuit.

Reference numeral 16 designates a signal coil for generating an ignitionsignal in synchrony with the rotation of the engine. The signal coil hasone end connected via a diode 17 and a resistor 18 with the gate of thethyristor 4, as well as to ground via a diode 19 and a resistor 20, andit has the other end thereof grounded. Reference numeral 21 designatesan ignition timing calculation circuit which receives the output signalof the signal coil 16 and the output signal of a retardation moderatingcircuit 32 which is to be described later for calculating a properignition timing, the ignition timing calculation circuit having anoutput terminal connected to the gate of the thyristor 4. Specifically,a junction between the diode 19 and the resistor 20 is connected with ajunction between one end of the resistor 22 and the base of thetransistor 23, the resistor 22 being connected at the other end thereofto a power source. The transistor 23 has a collector connected to thepower source via a resistor 24 as well as to a set terminal S of aflip-flop 25, and it also has an emitter connected to ground. Theflip-flop 25 has a Q output terminal connected via resistor 26 to anegative input terminal of an operation amplifier 27. A capacitor 28 isconnected between the negative input terminal and the output terminal ofthe operation amplifier 27. The operational amplifier 27 has a positiveinput terminal connected to the output terminal of the retardationmoderating circuit 32. The output terminal of the operational amplifier27 is connected to a negative input terminal of a comparator 29 whichhas a positive input terminal connected to the power source. Thecomparator 29 has an output terminal connected to the gate of thethyristor 4 via a capacitor 30, and to a reset terminal R of theflip-flop 25.

Reference numeral 31 designates a throttle sensor operatively connectedwith a throttle valve, which operates to adjust the amount of intake airsucked into the engine, for sensing the opening degree of the throttlevalve. The throttle sensor 31 generates an output voltage whichincreases as the throttle valve is driven in the closing direction A,and decreases as the throttle valve is driven in the opening directionB.

The retardation moderating circuit 32 comprises an integration circuitincluding a resistor 33, a capacitor 34 and a diode 35 which isconnected in parallel with the resistor 33 with its cathode connectedwith the output side of the throttle sensor 31.

Now, the operation of this embodiment will be described hereinbelow. Theoutput of the generator coil 1 is rectified by the diode 2 and chargedto the capacitor 3. The signal generator 16 generates an ignition signalin synchrony with the rotation of the engine. The signal generatoroutput contains a positive pulse, which is directly imposed on the gateof the thyristor 4 through the diode 17, and a negative pulse, which isinputted to the ignition timing calculation circuit 21. When a negativeignition signal is inputted to the ignition timing calculation circuit21, the transistor 23 is turned off to set the flip-flop 25 whereby thecapacitor 28 begins to discharge through the Q output terminal of theflip-flop 25, resistor 26, capacitor 28 and the output terminal of theoperational amplifier 27. When the output voltage of the operationalamplifier 27 becomes lower than a reference voltage V₁ which is imposedon the positive input terminal of the comparator 29, the output signalof the comparator 29 changes form the low level "0" to the high level"1". The high level output of the comparator 29 is then differentiatedby the capacitor 30 and imposed on the gate of the thyristor 4 as anignition timing control signal. At the same time, the flip-flop 25 isreset so that the output at the Q output terminal thereof changes fromthe high level "1" to the low level "0", thus interrupting the dischargeof the capacitor 28. At this time, current begins to be supplied to thecapacitor 28 through the output terminal of the operational amplifier27, capacitor 28, resistor 26 and the Q output terminal of the flip-flop25. Subsequently, when the output voltage of the operational amplifier27, which increases in accordance with the discharge of the capacitor28, exceeds the reference voltage V₁ at the positive input terminal ofthe comparator 29, the output level of the comparator 29 changes from"1" to "0". The discharging current continues to flow until a nextignition signal is inputted to the ignition timing calculation circuit21.

Here, it is to be noted that the interval in the engine rotational angleor crank angle between the instant when an ignition signal is inputtedto the ignition timing calculation circuit 21 and the instant when acorresponding ignition timing control signal is outputted is expressedas a linear function of the output voltages V₂ of the retardationmoderating circuit 32. That is to say, the higher the output voltage V₂,the greater the ignition timing control signal moves in theignition-retarding direction, whereas the lower the output voltage V₂,the greater the ignition timing control signal moves in theignition-advancing direction. The thyristor 4 is made conductive byeither of an ignition timing control signal and an ignition signal ofthe signal coil 16, causing the capacitor 3 to discharge. As a result,current flows from the capacitor 3 to the primary winding 6 of theignition coil 5 to produce a high voltage on the secondary winding 7 sothat the spark plug 8 can spark at a proper ignition time.

Although the output voltage V₂ of the retardation moderating circuit 32varies in dependence upon the output of the throttle sensor 31, the rateof change of the output voltage of the output voltage V₂ to the throttlesensor output when the throttle opening changes in the closing directionis different from that when it changes in the opening direction.Specifically, as the throttle valve moves from the fully closed positionA to the fully open position B, the output voltage of the throttlesensor 31 decreases and the capacitor 34 discharges through the diode 35so that the output voltage V₂ of the retardation moderating circuit 32decreases rapidly. On the other hand, as the throttle valve moves fromthe fully open position B to the fully closed position A, variations inthe output voltage of the throttle sensor 31 are integrated so that theoutput voltage V₂ of the retardation moderating circuit 32 increasesgradually. Accordingly, when the throttle opening changes in the manneras shown in FIG. 3(a), the ignition timing follows the change ofthrottle opening in the ignition-advancing direction, but it changesgradually in the ignition-retarding direction, as clearly seen from FIG.3(b).

Thus, when the operation of the marine engine is suddenly changed from aforward dirve to a rearward dirve, the throttle valve is held in thefully closed state during the time when the engine is changed from theneutral condition into the rearward drive condition. At this time,ignition takes place at a crank angle in advance of the maximumretardation angular position. Accordingly, since the engine is switchedinto the rearward driving operation under this state, there is no dangerof the stable engine operation being impaired even if the engine isabruptly loaded, thus preventing engine stall upon change in engineoperation.

FIG. 4 shows a circuit diagram of a second embodiment of the presentinvention. In this embodiment, a timer circuit 36 is provided betweenthe ignition timing calculation circuit 21 and the gate of the thyristor4. Specifically, the comparator 29 has an output terminal connected to afirst input terminal of an AND gate 37 which has a second input terminalconnected to a junction between a resistor 37 and a capacitor 39 whichare connected in series with the power source and ground. The AND gate37 has an output terminal connected via capacitor 30 to the gate of thethyristor 4. The respective arrangements other than the above of thisembodiment are similar to those of the previous embodiment, and hencethe corresponding parts are designated by the same symbols, omitting afurther explanation thereof.

Next, the operation of the ignition timing control apparatus of thissecond embodiment as constructed above will be described. When theengine is started, the throttle valve is fully closed and the outputsignal of the throttle sensor 31 is at the high voltage level. At thistime, the capacitor 34 of the retardation moderating circuit 32 is in adischarged condition and the output voltage V₂ of the retardationmoderating circuit 32 is substantially zero. Since the capacitor 34 ischarged through the resistor 33, however, the output voltage V₂ of theretardation moderating circuit 32 increases gradually. That is, evenwhen the throttle valve is in the fully closed position, the outputvoltage V₂ of the retardation moderating circuit 32 remains below aspecified voltage corresponding to the fully closed position of thethrottle valve for a predetermined time from the engine starting periodso that it outputs a signal in the throttle opening direction. As aresult, the ignition timing calculation circuit 21 outputs an ignitiontiming control signal which is an ignition-advancing signal.

Normally, ignition timing is retarded during the engine starting periodbecause, otherwise, there will be a defect that stable rotation of theengine after having been started is imparied. Thus, in this embodiment,the timer circuit 36 operates to disable the output of the ignitiontiming calculation circuit 21 for a predetermined time from the enginestarting period so that ignition can take place by a positive outputpulse of the signal coil 16. That is, the input voltage at the secondinput terminal of the AND gate 37 is held at the low level for thepredetermined time after power is turned on for engine starting, andtherefore even if an ignition timing control signal in theignition-advancing direction is inputted to the first input terminal ofthe AND gate 37, the output of the AND gate 37 remains at the low level.The predetermined time set by the timer circuit 36 is usually 2-5seconds, this being done by selecting an appropriate resistance and anappropriate capacitance for the resistor 38 and the capacitor 39. Afterthis time has elapsed, normal ignition timing control is carried out bythe output signal of the ignition timing calculation circuit 21.

FIG. 5 shows a circuit diagram of a third embodiment of the presentinvention which is equipped with a compensation circuit 40 for raisingthe output voltage V₂ of the retardation moderating circuit 32 to aprescribed level for a predetermined time from the engine startingperiod. In this FIGURE, 41 designates a comparator which has a negativeinput terminal connected with a junction between a resistor 42 and acapacitor 43, and a positive input terminal connected with a junctionbetween resistors 44, 45. The serially connected resistor 42 andcapacitor 43 and the serially connected resistors 44, 45 are connectedwith the power source. The comparator 41 has an output terminalconnected via a diode 46 to the output terminal of the retardationmoderating circuit 32. The respective arrangements other than the aboveof this embodiment are similar to those of FIG. 2.

With the ignition timing control apparatus as constructed above, duringengine starting, the output voltage of the throttle sensor 31 is at thehigh level, as described before, but the output voltage V₂ of theretardation moderating circuit 32 is held at zero because the capacitor34 is in the discharged condition. In this state, however, when thepower is turned on for engine starting, a voltage divided by theresistors 44, 45 is imposed on the positive input terminal of thecomparator 41 of the compensation circuit 40, the voltage at thenegative input terminal of which is held lower than the voltage at thepositive input terminal for a predetermined time (e.g., 1 second or lessin this embodiment) which is determined by a time constant with whichthe capacitor 43 is charged, the time constant being set by the resistor42 and capacitor 43. Therefore, the comparator 41 generates an outputsignal of the high voltage level which is fed to the output terminal ofthe retardation moderating circuit 41 whereby the output voltage V₂thereof immediately rises. As a result, the ignition timing calculationcircuit 21 generates an ignition timing control signal in the ignitionretarding direction so as to prevent the ignition timing from beingexcessively advanced. Thereafter, when the voltage at the negative inputterminal of the comparator 41 increases above the positive terminalvoltage, the output terminal thereof becomes low. Also, the outputvoltage of the retardation moderating circuit 32 is blocked by the diode46 so that ignition timing is therafter controlled in the same manner asin the first embodiment. In addition, in this embodiment, since thenormal ignition timing control is resumed in a relatively short periodof time, followability of the throttle valve after engine starting isaccordingly improved.

As described in the foregoing, according to the present invention, aretardation moderating circuit is provided which functions, when theopening degree of a throttle valve is changed in the closing direction,to move ignition timing in the ignition-retarding direction moregradually than the change in the throttle opening. This serves toprevent engine stalling which would otherwise occur at such a time aswhen a marine engine is changed into the rearward diriving operation.

Further, if a timer circuit is provided, it is possible to preventignition from taking place at an excessively advanced ignition timingduring the engine starting period, ensuring stable engine startingoperation.

Moreover, if a compensation circuit is provided, it is possible toperform stable engine starting operation as well as improvefollowability of a throttle valve after engine starting.

I claim:
 1. An ignition timing control apparatus comprising a generatorcoil and a signal coil each driven by an engine for generating anoutput, an ignition capacitor being charged by the output of saidgenerator coil and being discharged through a switching element inresponse to the output signal of said signal coil, an ignition coil forgenerating a high voltage by a discharging current of said capacitor soas to spark an ignition plug, a throttle sensor for outputting an outputsignal corresponding to the opening degree of a throttle valve, anignition timing calculating circuit for calculating an ignition timingcorresponding to the output of said throttle sensor with the outputsignal of said signal coil being taken as a reference, and supplying anignition timing control signal to said switching element, and aretardation moderating circuit for gradually changing the output of saidthrottle sensor supplied to said ignition timing calculation circuitwhen said throttle valve is driven in the closing direction.
 2. Anignition timing control apparatus as claimed in claim 1, wherein saidthrottle sensor is constructed such that it generates a voltage which isin inverse proportion to the opening degree of said throttle valve, andsaid retardation moderating circuit comprises an integration circuit forintegrating the output voltage of said throttle sensor, and a diodeconnected in parallel with a resistor of said integration circuit withsuch a polarity as to block the output voltage of said throttle sensor.3. An ignition timing control apparatus as claimed in claim 1 or 2,further comprising a timer circuit for detecting an engine startingperiod, and disabling the output of said ignition timing calculationcircuit for a predetermined time from the detection of the enginestarting period so that the output signal of said signal coilconstitutes the ignition signal during the engine starting period.
 4. Anignition timing control apparatus as claimed in claim 1 or 2, furthercomprising a compensation circuit for detecting an engine startingperiod and raising the output voltage of said retardation moderatingcircuit to a prescribed level for a predetermined time from thedetection of the engine starting period.